Composite polymeric material having high resistance to impact energy

ABSTRACT

A composite material with high resistance to impact energy, comprising an expanded polymer selected among polystyrene, polypropylene, copolymer of polyphenylene oxide and polystyrene and mixtures thereof, dispersed in a resin chosen among melaminic resin, phenolic resin and polyurethane resin and mixtures thereof.

[0001] This is a continuation-in-part application of U.S. applicationSer. No. 09/100,349, filed on Jun. 19, 1998.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to a composite polymeric materialhaving high resistance to impact energy.

[0003] Specifically, the present invention relates to a compositepolymeric material, to the corresponding preparation process and tomanufactured articles having high impact energy absorption.

[0004] Currently, manufactured articles for automotive parts capable ofabsorbing impact energy, such as structures for vehicle interiors andexteriors, motorcycle crash helmets and others, are made of a singlematerial having a polymeric base, such as expanded polystyrene, expandedpolypropylene, or polyurethane foams.

[0005] These manufactured articles are generally produced with a moldingtechnology which entails injecting an expandable polymer into a moldhaving a preset shape and then expanding the polymer in the presence ofcatalysts and/or expansion agents. At the end of the expansion, thepolymer hardens and acquires the preset shape of the mold.

[0006] In particular, in the production of polyurethane manufacturedarticles, polyisocyanates and polyesters or glycols are injected intothe mold and are made to polymerize in the presence of catalysts andexpansion agents. During polymerization, the polyurethane foam formsand, by expanding, takes the shape of the mold.

[0007] However, manufactured articles resistant to impact energy made ofa single polymeric material produced according to conventionaltechnology are not free from having drawbacks in use, mainly due to thefact that they are made of a single polymeric material which does notprovide an adequate resistance response to the impact and to the shockwave. In particular, the only variable that is available to the designeris the density of the material.

[0008] For example, impact-resistant manufactured articles made of asingle polymer according to the prior art, particularly expandedpolystyrene helmets for motorcycles, have the drawback that they losetheir impact-resistance characteristics after a single impact thatcauses a permanent deformation of the structure.

[0009] In the case of fenders for cars or of motorcycle helmets,permanent deformation after an impact accordingly compromises theirsafety characteristics, forcing the user to replace the manufacturedarticle.

SUMMARY OF THE INVENTION

[0010] One of the aims of the present invention is to eliminate orsubstantially lessen the drawbacks of the prior art.

[0011] Another object of the present invention is to provide a compositepolymeric material which has high-level impact energy resistancecharacteristics and has a long life.

[0012] A further object of the present invention is to provide acomposite polymeric material which is simple to produce and does notentail high production costs.

[0013] Yet another object is to provide a manufactured article made ofcomposite polymeric material which combines low weight with highmechanical strength characteristics.

[0014] Another object of the invention is to provide a method forproducing manufactured articles made of an impact-resistant compositematerial whose execution entails modest operating and energy-relatedcosts.

[0015] With the foregoing and other objects in view, there is provided,in accordance with a first aspect of the present invention, a compositematerial comprising a pre-expanded polymer, preferably in granular form,selected from the group consisting of polystyrene, polypropylene, acopolymer of polystyrene with a melting point above 90° C. and mixturesthereof, dispersed in a resin selected from the group consisting ofmelaminic resin, phenolic resin, polyurethane resin and mixturesthereof, the polyurethane resin being the preferred one among them. Theexpression “polystyrene copolymer” denotes a product of polymerizationof polystyrene with another polymer or an alloy of polystyrene withanother polymer.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0016] Among polystyrene copolymers having a melting point above 90° C.,preference is given to those with a melting point above 100° C.; amongthese, particular preference is given to the copolymer of polyphenyleneoxide (PPO) and polystyrene (PS). By way of example, mention is made ofthe copolymer of polyphenylene oxide and polystyrene marketed under thetrade-name NORYL EF (in granules or expandable beads) by the GeneralElectric Co., USA, and of the product of the Huntsman Chemical Co.,Chesapeake, Va., USA, marketed under the trade-name GECET (polymericalloy of PS-PPO).

[0017] The pre-expanded polymer used in the present invention hasadvantageously been subjected beforehand to an expansion process and hasa granular, spherical or bead-like shape.

[0018] The composite polymeric material according to the presentinvention preferably consists of a uniform dispersion of pre-expandedgranules or beads in a matrix of a polyurethane, melaminic or phenolicresin.

[0019] Preferably, the polyurethane used in the present invention isobtained by condensation of an isocyanate or polyisocyanate with acompound possessing active hydrogen, both selected so as to have thefollowing characteristics:

[0020] low reactivity; a delayed polymerization time of at least about30 seconds allows the two components still in a fluid state to easilyreach the lowest part of a mold wherein pre-expanded granules or beadsare packed and then initiate the polymerization phase, so that when thepolymerisation phase is completed, all (or almost all) the voids amongthe beads are filled with polyurethane (about 50% of the total volume ofthe mold);

[0021] optimal cohesion properties and adherence to the expanded beads;

[0022] optimal mechanical resistance;

[0023] low initial viscosity of the mixture of the two components,allowing an easy penetration in the voids created among the expandedbeads;

[0024] high expansion capacity allowing the complete filling of the freespaces so as to obtain a homogeneous structure of the compositematerial;

[0025] high heat resistance;

[0026] high self-extinction.

[0027] Examples of such components are the isocyanate marketed by DowChemical Co., USA under the name VORACOR CD 526 and the polyol marketedby Dow Chemical Co., USA, under the name VORACOR CD 443.

[0028] The composite material having a polymeric base, according to thepresent invention, has high impact energy absorption because, followingan impact, the impact energy is transmitted along the resinousstructure, which has acquired a cellular structure whose cellsinternally contain the expanded polymeric granules, which undergoelastic deformation and considerably contribute to damping propagationof the shock wave and to ensuring the preservation of impactenergy-absorbing properties even with subsequent impacts.

[0029] In view of these characteristics, the composite materialaccording to the invention is particularly suitable to providelightweight manufactured articles having high mechanical strength andresistance to impact energy and to repeated impacts.

[0030] Said manufactured articles comprise, in variable amounts, thecomposite material according to the invention, alone or associated withother impact-resistant materials.

[0031] Comparative tests have shown that the manufactured articlesaccording to the invention have higher energy absorption thanpolystyrene and, for an equal density with respect to polyurethane, aremore resistant to impact energy and to repeated impacts.

[0032] The manufactured articles according to the present invention canbe entirely made of the above-described composite material or areconstituted by multilayer structures in which, for example, one or morelayers are made of the composite material and the remaining layers aremade of other materials (polymeric and nonpolymeric).

[0033] According to another aspect of the present invention, saidmanufactured article is a liner for helmets, for example of the type formotorcycles, cars, work or sport. Helmet liners manufactured with thecomposite polymeric material according to the invention are highlyresistant to impact energy and in particular maintain theirimpact-resistance characteristics substantially unchanged even after oneor more impacts.

[0034] In particular, it has been observed that the permanentdeformation of the surface structure of the manufactured articleaccording to the invention produced by a medium-energy impact does notcompromise, except to a limited extent, its strength and safetycharacteristics, making them suitable for prolonged use.

[0035] According to a further aspect, the present invention relates to alife preserver which comprises the composite material described above.Advantageously, said life preserver is constituted by a core made ofvery hard polymeric material or wood or steel, covered with a layer ofthe composite material according to the invention. The life preserveraccording to the invention has a weight which can be likened to that oflife preservers of the prior art together with high impact resistance.

[0036] In accordance with yet another aspect of the present invention,said manufactured article is an automotive interior, such as doorpaddings, door panes, knee bolsters, head restraint systems, sun vizors,instrument panels, rear parcel shelves, or an automotive exterior suchas bumpers, body supports or an automotive cavity filling.

[0037] In accordance with another aspect of the present invention, amethod for producing manufactured articles made of composite material isprovided, said method comprising the steps of:

[0038] injecting into a mold a pre-expanded polymer selected from thegroup consisting of polystyrene, polypropylene, polystyrene copolymerwith a melting point above 90° C. and mixtures thereof, and in theninjecting a resin or the reagents that polymerize into a resin selectedfrom the group consisting of polyurethane resin, phenolic resin,melaminic resin and mixtures thereof;

[0039] expanding said resin inside the mold, dispersing saidpre-expanded polymer therein.

[0040] Preferably, the pre-expanded polymer is supplied in the form ofgranules or beads which have dimensions between 3 and 10 mm and thepolymerization reaction to generate said resin occurs at a temperaturebetween 70 and 140° C.

[0041] According to a preferred embodiment of the method according tothe invention, the following operating steps are performed in sequence:

[0042] filling a mold with granules of a pre-expanded polymer selectedfrom the group consisting of polystyrene, polypropylene, copolymer ofpolyphenylene oxide and polystyrene and mixtures thereof;

[0043] subsequently injecting in the mold an isocyanate or apolyisocyanate and a compound possessing active hydrogen thereby theyare filled in void spaces among the granules,

[0044] condensing said isocyanate or polyisocyanate with a compoundpossessing active hydrogen to generate, by polymerizing, a polyurethanefoam which, by expanding, substantially completely fills the spacesamong the pre-expanded polymer granules.

[0045] It has been observed that by initially filling the mold with thepre-expanded polymer in granular or bead form and then injecting thepolyurethane, it is possible to determine the weight and therefore thedensity of the manufactured article.

[0046] Preferably, the reaction for condensation between the isocyanateand the compound possessing active hydrogen determines a temperaturebetween 70 and 140° C. In the execution of the method it is possible touse expansion agents, additives and catalysts for the condensationreaction capable of accelerating polymerization and resin hardeningtimes.

[0047] The reagents are preferably injected by usingpositive-displacement pumps with a variable rotation rate and a mixerfor mixing the two streams of reagent.

[0048] The term “compound possessing active hydrogen” denotes a compoundthat may be replaced by sodium and with a few compounds having hydrogenatoms not readily replaced by sodium. In the reaction with saidcompounds possessing active hydrogen, the hydrogen atom becomes attachedto the nitrogen of the isocyanate and the remainder of theactive-hydrogen compound becomes attached to the carbonyl carbon. Saidcompounds possessing active hydrogen include compounds having amino,hydroxyl, carboxyl groups, particularly polyesters, polyethers andpolyols, the last being preferred.

[0049] The polyurethane condensation or foaming step advantageouslyentails expansion times lasting between 10 and 15 minutes, during whichthe polyurethane foam expands into the empty volume between the polymergranules.

[0050] In accordance with an embodiment of the method according to theinvention, the mold is filled initially with the pre-expanded polymer.

[0051] Preferably, the mold is initially completely filled with beads ofexpanded material with suitable dimensions and bulk density.

[0052] The polyurethane resin suitable for use in the present inventionhas a high fluidity and a delayed polymerization time, of at least 30seconds, so as to allow the passage of the resin through all theexpanded material filled in the mold, in the void spaces among thebeads.

[0053] Moreover, the polyurethane resin used in the present inventionhas a high polymerization heat.

[0054] Due to the properties of the isocyanate and active hydrogencontaining compound, as indicated above, in particular due to their highfluidity and low polymerization time, the isocyanate and the activehydrogen containing compound are filled in substantially all the emptyspaces among the pre-expanded polymer beads.

[0055] Due to the granular (or bead-like) shape of the polymer, emptyspaces remain between the granules and are gradually filled during theexpansion of the polyurethane resin. A composite material is thusobtained which has a substantially uniform distribution of thepre-expanded polymer granules.

[0056] It has been observed that the pre-expanded polymer granules orbeads, during the exothermic reaction for the polymerization of thepolyurethane resins, behave differently according to the chemical natureof the polymer being used.

[0057] In particular, when granules or beads of expanded polypropyleneor of an interpolymer of polyphenylene oxide and expanded polystyreneare used, the polyurethane condensation reaction can occur at atemperature between 100 and 140° C. without causing their melting orbreakdown. The polypropylene beads, amalgamated in the polyurethanefoam, by being filled with air, can compress under the impact energy andthen resume their initial position, thus dissipating the kinetic energy.It has been observed that the resulting composite material has thehighest impact-resistance characteristics.

[0058] Instead, when polystyrene granules or beads are used in theprocess, the generation of heat (T=80-100° C.) typical of the exothermicpolymerization reaction of polyurethane causes them to melt. Thegranules, under the heat, melt inside the polyurethane foam, creatingvoids.

[0059] The granules or beads used in the process according to theinvention are expandable polymers, expanded for example by subjectingpolymeric expandable beads to a pre-expansion in a pressurized vesselusing dry saturated steam. Then the pre-expanded beads are subjected toa drying step and to a maturing stage to compensate for the temporaryvacuum in the cell structure after pre-expansion. This is achieved, forexample, by blowing the prefoam into an air-permeable silo. Aftersufficient air has been diffused into the cells, the matured beads arestable and ready for processing.

[0060] The matured prefoam is blown into a mold of the desired shape,preferably until the mold is almost completely filled.

[0061] The pre-expanded granules used in the invention preferably have adensity between 10 and 80 g/l, while the resins used preferably have adensity between 20 and 400 g/l.

[0062] The method according to the present invention providesmanufactured articles made of composite material with modest operatingand energy-related costs. In particular, operating costs are reducedthanks to the possibility of using resin molds which are commonlycommercially available at low cost. Molds used in the field of theinvention are preferably thermostat-controlled, so as to maintain atemperature, during the resin polymerization step, that is lower thanthe melting temperature of the foamed polymer described above.

[0063] Energy expenditure is reduced due to the low operatingtemperatures of the processing plant.

[0064] According to an embodiment of the method according to theinvention, manufactured articles of preset shape, such as for exampleouter shells, reinforcement elements, hooks, nets etcetera, are placedbeforehand in the molds.

[0065] The following examples are given merely to illustrate the presentinvention and must not be understood as limiting its scope as defined inthe accompanying claims.

EXAMPLE 1

[0066] Three types of helmet were manufactured: each helmet had an outershell made of glass fiber and an inner liner having a differentcomposition:

[0067] 1. Inner liner made of polystyrene with a density of 60 g/l;

[0068] 2. Inner liner made of polyurethane resin with a density (freeexpansion) of 60 g/l;

[0069] 3. Inner liner made of the composite material according to theinvention, constituted by an interpolymer of polystyrene and phenylenepolyoxide (GECET) dispersed in polyurethane foam produced bycondensation between polyol (VORACOR CD 443) and isocyanate (VORACOR CD526), both of marketed by the Dow Chemical Co., USA.

[0070] The three types of helmet were subjected to impact testingaccording to the SNELL 95 standard commonly used in helmet testing.

[0071] The conditioning temperature was 50° C. Peak Peak Peak <300 g<300 g <300 g Inc Height Region 1 2 3 HEMI 318 B 222 353 209 ″ 235 B 449500 210 ″ 318 xDx 136 214 195 ″ 233 xDx 242 291 198 ″ 318 P 264 219 235″ 233 P 300 243 192 ″ 318 R 177 166 195 ″ 233 R 324 176 168 ″ 318 xSx146 245 154 ″ 233 xSx 249 361 213

[0072] B,B first and second drop test on the front region;

[0073] xDx, xDx first and second drop test on the right lateral region;

[0074] P, P first and second drop test on the upper region;

[0075] R, R first and second drop test on the rear region;

[0076] xSx, xSx first and second drop test on the left lateral region.

[0077] The helmet produced by using the composite material according tothe invention had, following the impact, considerably smaller peaks thanfound when using helmets having a conventional type of inner liner.

[0078] Comparative tests show that the material according to theinvention is particularly suitable to form manufactured articles inwhich high impact resistance is required.

EXAMPLE 2

[0079] A method for manufacturing the composite polymeric materialaccording to the invention.

[0080] 160 g of expanded beads of Noryl EF (G.E. Co., USA) are injectedin a resin mold (volume 8 liters) provided with an air vent and shapedlike an automotive bumper. An air injector then injects 100 parts byweight (100 g) of VORACOR CD 443 polyol and 110 parts by weight (110 g)of VORACOR 526 isocyanate.

[0081] The polymerization reaction produces a polyurethane foam whichexpands completely in approximately 12 minutes at a temperature ofapproximately 110° C., filling the voids among the foamed polymericbeads.

[0082] The mold is then opened and the manufactured article is extractedand finished according to conventional finishing methods which includecoloring and decorative methods for modifying and peeling the surface.

1. A method for producing manufactured articles made of compositematerial, comprising the steps of: injecting into a mold a pre-expandedpolymer selected from the group consisting of polystyrene,polypropylene, polystyrene copolymer with a melting point above 90° C.and mixtures thereof, and a resin selected from the group consisting ofpolyurethane resin, phenolic resin, melaminic resin; polymerizing saidresin to form a polymerized resin in which the pre-expanded polymer isdispersed.
 2. A method according to claim 1, wherein thepolycondensation reaction occurs at a temperature between 70 and 140° C.3. A method for producing manufactured articles made of compositematerial, comprising the steps of: filling a mold with granules of apre-expanded polymer in granular form, selected from the groupconsisting of polystyrene, polypropylene, copolymer of polyphenyleneoxide and polystyrene and mixtures thereof; subsequently injecting inthe mold an isocyanate and a compound possessing active hydrogen therebythey are filled in void spaces among the granules; condensing saidisocyanate with said compound possessing active hydrogen to yield apolyurethane foam which, by expanding, substantially completely fillsthe spaces among the pre-expanded polymer granules.
 4. A methodaccording to claim 3, wherein the condensation reaction takes place at atemperature between 70 and 140° C.
 5. A method according to claim 3,wherein the mold is initially completely filled with said pre-expandedpolymer in bead form.
 6. A method according to claim 3, wherein saidcompound possessing active hydrogen is a polyol.
 7. A method accordingto claim 3, wherein the pre-expanded polymer is a copolymer ofpolyphenylene oxide and polystyrene or expanded polypropylene and inthat the polyurethane condensation reaction occurs at a temperaturebetween 100 and 140° C.
 8. A method according to claim 3, wherein saidexpanded product has a density between 10 and 80 g/l.
 9. A methodaccording to claim 3, wherein said polyurethane resin has a densitybetween 20 and 400 g/l.
 10. A method according to claim 3, wherein saidmold includes a manufactured article having a preset shape.
 11. Themethod according to claim 3, wherein the isocyanate and the activehydrogen containing compound having a polymerization time higher than 30seconds.
 12. A composite polymeric material having high resistance toimpact energy comprising expanded beads of polypropylene dispersed in aresinous matrix selected from the group consisting of melaminic resin,phenolic resin, polyurethane resin and mixtures thereof.
 13. Thematerial according to claim 12 wherein the resinous matrix is apolyurethane resin obtained by polycondensation of an isocyanate orpolyisocyanate with a compound containing active hydrogen.
 14. Thematerial according to claim 13, wherein the isocyanate or polyisocyanateand the active hydrogen containing compound have a polymerization timehigher than 30 seconds.
 15. An impact-resistant manufactured articleincluding a composite polymeric material having high resistance toimpact energy comprising expanded beads of polypropylene dispersed in aresinous matrix selected from the group consisting of melaminic resin,phenolic resin, polyuretane resin and mixtures thereof.
 16. Theimpact-resistant manufactured article according to claim 15, whereinsaid article is an inner protective liner of a helmet.